It is well known from the past that release liners having release properties relative to sticky materials, typically pressure-sensitive adhesives are prepared by forming a cured coating having release properties on the surface of substrates such as paper, laminated paper and plastic film. Among the materials used for forming a cured coating having release properties are silicone compositions. For example, JP-A S62-86061 discloses a silicone composition comprising an alkenyl-containing organopolysiloxane, an organohydrogenpolysiloxane, and a platinum base compound.
Silicone compositions of this type are still predominant at the present because of their cure behavior and pot life. However, a problem has been pointed out that the adhesion between the cured coating and the substrate is not regarded sufficient. This poses limitation on the type of substrate that can be coated and necessitates pretreatment of the substrate.
Under the recent trend of available substrates, the use of plastic film substrates is increasing because of uniform and stable quality, high smoothness, and film thinness. As a wide variety of substrates are now available in the market, the requirement to improve the adhesion of silicone compositions to substrates becomes more desirable than ever.
Proposals for improving adhesion have also been made from the side of silicone compositions. For example, one attempt to use more adhesive materials includes blending of organic resins and addition of silane coupling agents. However, this attempt is utilized only under limited conditions because release properties are otherwise degraded. Another method is to modify the base polymer structure of the silicone composition. Base polymers having a branched structure containing RSiO3/2 units are disclosed in JP-A S63-251465, JP-B H03-19267, JP-A H09-78032, and JP-A H11-193366. This method is mainly intended for light release upon high-speed peeling and for effective cure while some improvement in adhesion is achieved as a secondary effect. Also JP-A 2000-169794 and JP-A 2000-177058 propose the combined use of a solvent type silicone composition and a solventless silicone composition, thereby achieving the effect of reducing peeling speed dependence without modifying the base polymer structure. With respect to adhesion, this proposal does not surpass the existing solvent type silicone compositions.
As discussed above, there is available in the art no appropriate technique capable of improving the adhesion of a silicone composition without affecting the release properties thereof.